1. Field of the Invention
This invention relates to a chuck assembly, more particularly to a chuck assembly which is easy to fabricate and convenient to operate.
2. Description of the Related Art
FIG. 1 illustrates a conventional chuck assembly 10 for holding a tool bit, such as a drill bit 11. After the drill bit 11 is inserted into the chuck assembly 10 for operation or when the drill bit 11 is to be removed from the chuck assembly 10 for replacement, a chuck key 12 with a rotary gear must be operated to tighten or loosen the drill bit 11. Operation of the chuck assembly 10 is therefore inconvenient and unsatisfactory.
Referring to FIG. 2, another conventional chuck assembly 20 is shown to include a chuck body 21, a drive ring 22, and a plurality of clamping pieces 23. The chuck body 21 is formed with an insert hole 211 at a front end thereof for receiving a section of a tool bit, such as a drill bit 212. The chuck body 21 is further formed with a plurality of inclined elongated guiding channels 213 which extend from a rear end of the chuck body 21 to the front end, and which converge forwardly to communicate with the insert hole 211. Each of the guiding channels 213 has a generally circular cross-section. The clamping pieces 23 are received in the guiding channels 213, respectively. Each of the clamping pieces 23 has a rear section with a generally semi-circular cross-section and an outer side surface formed with an external thread 231. The chuck body 21 is further formed with an annular peripheral groove 214 for accessing the guiding channels 213. The drive ring 22 is received rotatably in the peripheral groove 214 of the chuck body 21, and is formed from two complementary ring parts. The drive ring 22 has an inner surface formed with an internal thread 221 for meshing with the external threads 231 of the clamping pieces 23. Accordingly, by rotating the drive ring 22, the clamping pieces 23 are movable forwardly and rearwardly in the guiding channels 213 by virtue of the engagement between the internal thread 221 of the drive ring 22 and the external threads 231 of the clamping pieces 23 in order to loosen or tighten the drill bit 212.
The conventional chuck assembly 20 suffers from the following drawbacks:
1. Since the clamping pieces 23 are slidable within the guiding channels 213, and since the clamping pieces 23 have curved outer surfaces to conform with the curved inner surfaces of the guiding channels 213, the cross-section of each of the guiding channels 213 is slightly larger than a largest cross-section of the respective one of the clamping pieces 23 in order to permit smooth movement of the clamping piece 23 along the guiding hole 213. As such, when the drill bit 212 is clamped by the clamping pieces 231, and when the chuck body 21 is rotated axially with a relatively high speed while working on a work piece (not shown), undesired movement or axial rotation of the clamping pieces 23 in the guiding channels 213 will result since the outer surfaces of the clamping pieces 23 are not restricted by the inner surfaces of the guiding channels 213. This may prevent the clamping pieces 23 from meshing precisely with the drive ring 22 and can cause damage to the clamping pieces 23 and to the external threads 231 formed on the clamping pieces 23. PA1 2. Formation of the guiding channels 213 that have curved and smooth inner surfaces, and of the clamping pieces 23 that have curved and smooth outer surfaces involve relatively complicated manufacturing and processing steps. Therefore, the chuck assembly 20 is relatively costly to fabricate.